Canned food recyclable thermal simulator

ABSTRACT

A method of measuring internal temperatures of canned foods under actual operating conditions by placing recyclable thermal simulators in each batch of canned foods during the actual processing. A recyclable thermal simulator device having the same thermal characteristics as the particular canned food being simulated. A method for manufacturing recyclable thermal simulators by equipping a container substantially identical to those simulated with a suitable temperature indicator, filling the container with a porous, open-celled, sponge-like matrix material, uniformly distributing a liquid of a pre-determined specific gravity throughout the matrix material by means of a partial vacuum usually identical to that drawn on the canned food simulated and sealing the container. Matching the thermal characteristics of different canned foods is generally accomplished primarily by varying the matrix density, the specific gravity of the liquid, and the percentage of open cells in the matrix material and by employing identical containers and drawing the same partial vacuums used by the canned foods simulated.

This invention relates to a novel method and device for measuring theinternal temperatures of canned foods during processing and the methodfor manufacturing such devices.

Historically, the conventional method of determining the internaltemperature of hermetically sealed solid foods during thermal processingis by spot-checking, which is the selection of one or more samples atrandom from each batch in commercial processing lines and thereafterinserting a stem-type thermometer through the can wall into thecentermost portion or coldest-spot of the product or that portion of thefood product slowest to attain the desired temperature. The spot-checkmethod has two primary disadvantages. The first is that it iseconomically costly and the second is the degree of inherent inacurracy.

From an economic standpoint spot-checking is costly because thecontainer is destroyed and the food product must be reprocessed into asubstantially lower profit product, such as from a canned ham to cannedluncheon meat. The reprocessing involves substantial labor costs for theunpacking, reprocessing and subsequent repacking of the product. Inaddition the end product is sold at a fraction of its original value.

The importance of accurately measuring the internal temperature ofcanned foods during processing is seen by the fact that insufficientheat processing will result in an improperly cooked product and mayresult in the growth of undesirable microorganisms which can produceproduct spoilage and/or illness to the consumer. Overcooking of theproduct is equally critical since, by its nature, it tends to adverselyaffect the organoleptic properties of the product and the consumerappeal of the product. Therefore it is seen that while it is essentialthat canned foods be heated to a critical minimum temperature, it isequally essential that the heating be kept within the critical maximumrange. It also follows that the heating be as uniform as practical forall portions of the product. To insure an accurate measurement for mostsolid type foods, the temperature must be recorded within 1/16th inch ofthe centermost portion or so-called coldest-spot. The food container isgenerally shaped to require a uniform penetration of the externallyapplied heat to avoid overcooking of any portion of the contents whileraising the temperature of the centermost portion to the requiredminimum.

The accuracy of the spot-check method is frequently impaired because itis not always possible to measure the internal temperature precisely atthe centermost portion of the product. Also, once the container of theheated product is punctured, the internal pressure is released. Thissudden pressure release causes the excess liquid surrounding the productwhich vaporizes during heating, to condense and drain to the bottom ofthe container. Also, the natural liquids chemically bound within theproduct may also be disrupted after the container is punctured.

A more recent innovation relating to the thermal testing is to cut acylindrical hole in a side wall of the container or at a point where thethermocouple can be inserted into the product. To insert a self-sealingtemperature measuring unit through the hole, the measuring unit isgenerally screwed into a leak-proof packing gland which is attached tothe periphery of the hole cut in the container. After the product hasbeen placed in the container, the measuring unit is thereafter insertedinto the centermost part of the product or a point equal distance fromthe opposite sides of the container, or in the coldest-spot. Finally thecanned product, with the thermocouple fitted in place is sealed underthe usual partial vacuum. Despite the increased accuracy in thepositioning of the thermal measuring unit into the centermost portion ofthe product, the disadvantages of this test method are similar to thoseof the spot-check method in that each test unit requires the same amountof reprocessing, handling, destruction of the container, the value lossof the meat, and is not recyclable.

A recent estimate of the cost resulting from government inspection, bothfederal and state, for a newly established canned ham operation,indicated that many thousands of dollars worth of supplies, labor andproduct devaluation would result from temperature checks of product inall aspects of the new processing lines. Normally in establishedproduction lines it is estimated that about 1/10th of one cent per poundof product is lost each year by many canning establishments as a resultof present methods of quality control and maintenance of federal andstate regulations. Samples are taken from each batch of certain foods,such as canned hams, for federal inspection of temperature control inaddition to those taken for normal in-house quality control by theprocessing plant. The number of destroyed units in a process batchgenerally runs between 2 and 3 units per basket or may have any numberof a variety of other type groupings depending on the process.

Accordingly, it is an object of the present invention to provide amethod for producing a reheatable, reusable thermostatic unit forinterdispersing with each batch of product in the same manner as testunits would normally be selected and which accurately duplicates orsimulates the internal operating conditions of the canned food productbeing heat processed.

It is another object of the present invention to provide a recyclabledevice for recording the internal temperature and/or pressure of cannedfood products while under actual processing conditions and to accuratelyrecord the highest temperature attained by the centermost portion of theproduct during heat processing and any carryover temperature duringchilling.

It is another object of the present invention to provide a method ofaccurately recording, by means of a recyclable simulator device, theinternal temperature of hermetically sealed canned food products within1/16th inch of the centermost portion of the canned product being heatprocessed.

It is another object of the present invention to provide materialssuitable for simulating the thermo-conductivity characteristics orK-factor of hermetically sealed solid type foods during conventionalcanning processing.

It is another object of the present invention to accurately duplicatethe liquid phase in the solid food simulated comprising suitable matrixmaterial such as rubber and plastic open cell foams and liquid media,which is capable of providing the same thermo-conductivitycharacteristics or K-factor of particular foods, including meats, duringthe actual processing conditions.

It is yet another object of the present invention to provide a method ofmeasuring the thermal conditions of food products during processing byproviding matrix materials having varying densities and havingvariations in the percentage of open cells; and a liquid systemcomprising solutions of varying concentrations, specific heat, and/orspecific gravities, in order to produce the same K-factor orthermo-conductivity characteristics of the food product being simulated.

It is still another object of the present invention to provide a methodof measuring the internal temperature of different canned meat productsduring processing by varying the percentage of open cells in the matrixmaterial, varying the density of the matrix material, varying thespecific gravity of a liquid system used to impregnate the matrixmaterial while under partial vacuum, so that a recyclable simulation ofa particular product is produced having the same thermo-conductivityrate or the same K-factor.

It is another object of the present invention to provide a cannedrecyclable simulator wherein the simulated food product is meat, thesimulator matrix is polyurethane having a density between from about 10to about 35 lbs. per cu. ft. and having from about 50 to about 75percent open cells and the liquid system is a suitable aqueous solutionhaving a specific gravity within the range of from about 1.0635 to about1.2296.

In general this invention relates to a recyclable simulator device formeasuring and/or recording the internal operating temperature of cannedfoods while under actual operating conditions. It particularly relatesto the discovery that certain foam materials, such as plastics andrubbers having an open cell structure, offer an excellent matrix whichwhen pregnated under a partial vacuum with a liquid system of aparticular specific density, will provide a thermo-conductivity curvecorresponding to that of a particular solid type food product whilebeing heated. By varying the specific gravity of different liquidsystems it was found that the thermo-conductivity or the K-factor of ahermetically sealed simulator device can be extended over a broad rangeto equal the K-factor of many different types of canned food products.The K-factor is further broadened by varying the densities of theporous, foam type materials such as rubber and/or plastics such aspolyurethane compounds and by varying the percentage of open cellswithin the matrix. The K-factor or thermo-conductivity of many solidfood products such as meats can be accurately duplicated by employingsuch a lightweight open celled material as a plastic foam known to havea K-factor substantially below that of the solid product beingsimulated.

Further objects and advantages will become apparent upon reading thefollowing detailed disclosure of a preferred embodiment of the inventionin conjunction with the drawing.

The drawing is a perspective view of an embodiment of the presentinvention showing a simulator device of a pear-shaped ham.

In the method of producing a canned product simulator it should be keptin mind that rather specific characteristics are required in a simulatedmaterial to accurately duplicate the internal conditions produced incanned products during cooking. It will be obvious to those skilled inthe art that producing thermal simulators for solid type canned foods ismore difficult than producing those for liquid type canned foods. Forexample, when cured meats are cooked there is a transfer of chemicallybound liquid present throughout the meat as the maximum temperature isreached. The conduction of heat throughout the meat is affected by thechanging basis of the liquid distribution. The liquid present in thecanned food product and simulator act as a prime conductor forexternally applied heat. For this reason it is much easier to produce asatisfactory simulator for canned foods which are essentially in aliquid state. Therefore, the examples herein are directed to solid typecanned foods; such as, comminuted meats as ground poultry, beef and/orpork luncheon meats; diced foods, such as, pressed ham or canned tuna;and, whole solid meat chunks; such as, canned hams or whole cannedchickens. Because it is more difficult to control and to duplicate themoisture content, hence the thermo-conductivity, of whole solid meatchunks as compared with comminuted and diced meat products into whichvarying amounts of liquids can more easily be incorporated, canned hamshave been selected to illustrate the utility of the present invention.These examples are cited merely as illustrative of the present inventionand are not intended as restricting the scope of the appending claims.Obviously, the greater the cost factor per unit of canned food, thegreater the incentive to employ such recyclable thermal simulators.

In the process of producing thermal simulators, it is preferred that thecontainer housing of the simulator be of substantially the same thermalconductivity and physical dimensions as that of the food container beingsimulated. This insures that the container wall will have the samethermo-conductivity characteristics and that the externally applied heatwill be conducted the same distance in the simulator as in the productbeing processed. For this reason, it is preferred to use the samecontainer for the simulator as that housing the canned food beingsimulated. The simulator containers are then filled with a porous, opencell matrix material having a predetermined percentage of open cells anddensity to which a suitable amount of a liquid system having apre-determined specific gravity, is added. The container is equippedwith any suitable device for measuring the internal temperature within1/16th inch of the centermost point or coldest-spot of the container.The container is then sealed under a partial vacuum and tested to verifyit has the same K-factor or thermo-conductivity ratio as the particularfood it simulates. Generally, it is preferred to have the same partialvacuum for the simulator as for the canned product being simulated.

In operation, for example, when foam type material or matrix 25, e.g.,rubber or plastic (polyurethane) are being compounded, it is feasible toform or cut the material in any desired shape which would simulate thesize and shape of a corresponding food contaner 10. The forming of thesematerials 25 is done so that no skin formation exists and the cellstructure is then more readily impregnated with liquids when sealedunder vacuum.

In addition to the usual rod or needle type thermocouple 15 any varietyof sealing device 20 or measuring devices may be attached to thesimulator container 10 such as those emitting an audible or an electricsignal. In the more sophisticated or automated processing operations, itis possible for an electronic signal to automatically initiate the nextprocessing step when the desired internal temperature has been attainedin the cooking step. Obviously, when a plurality of simulators areemployed in a single batch, each has the advantage of verifying theaccuracy of the other simulators.

Examples of open cell materials found to be particularly useful are thematrix of: cellulose acetate, epoxies, phenols, polyethylene, polyols,polyethers, polystyrene, silicones, urea-formaldehyde, and the vinylcompounds. Polyurethane materials having a lb. per cu. ft. density offrom about 10 to about 35 lbs. were found particularly useful induplicating the thermo-conductivity curves of canned meats, particularlywhen combined with liquid systems using various concentrations ofsucrose solutions of from about 10 to about 50 percent. An open cellmatrix made from foamed plastics or rubber having from about 50 to about75 percent open cells was found particularly useful in duplicating thethermo-conductivity of canned meats.

Liquid systems which are both easily accessible and low in cost andwhich have proved most satisfactory include sucrose, glycerine, sodiumchloride, sodium carbonate, sodium nitrate and solutions of otherchemicals having a specific gravity range of from about 1.0635 to about1.2296.

EXAMPLE I

Polyurethane having a density of 20 lbs. per cu. ft. and about 70percent open cells was impregnated with 16 percent aqueous sucrosesolution and placed in a 3 lb. pear-shaped ham container having astem-type thermometer positioned within to contact that portion of theinterior equal distance from all sides of the container. The containerwas then placed under a vacuum of 27.5 inches for a time sufficient toyield a uniform distribution of the solution throughout and thereaftersealed. The simulator was tested under actual operating conditionsagainst canned hams of the same size and weight and was found tosatisfactorily duplicate the thermo-conductivity curve of the canned hamproduct.

EXAMPLE II

Polyurethane having a density of 15 lbs. per cu. ft. and about 75percent open cells was impregnated with an aqueous solution of 55percent sucrose and placed in an 8 lb. pear-shaped ham container havinga stem-type thermometer placed to contact that portion of the interiorequal distance from all sides of the container. The container was thenplaced under a vacuum of 27.5 inches for a time sufficient to yield aweight equal to the same size cured ham and thereafter sealed. Thesimulator was tested under actual operating conditions against cannedhams of the same in size and weight and was found to satisfactorilyduplicate the thermo-conductivity curve of the canned ham product.

Similar tests were made with such products as canned whole chickens,tuna, and differet types of both diced and comminuted luncheon meatsusing foamed plastics and rubber having a matrix from about 50 to about75 percent open cells which when impregnated with liquids of a specificdensity of between about 1.0635 and about 1.2296 and placed in asuitable container under conventional vacuum, satisfactorily providedthe thermoconductivity curve equal to the solid type food product beingduplicated.

Obviously, many variations and modifications of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof and, therefore, only those limitations should be imposedas are indicated in the appended claims.

I claim:
 1. A permanently recyclable simulator device for duplicatingthe internal thermal characteristics of canned foods, said simulatorcomprising: a container of the same composition and physical dimensionsas the container for the food simulated, a porous open cell matrixmaterial positioned within and substantially filling said container, aliquid uniformly distributed throughout said matrix material when sealedunder vacuum, and a suitable thermal recording device permanentlyattached and extending through a wall of said container to 1/16th inchof a point equal distance from the interior walls thereof, the densityand the percentage of open cells of the matrix material in combinationwith the specific heat of the liquid uniformly distributed thereinproducing a thermal-conductivity constant substantially identical withthat of the canned food simulated.
 2. The device of claim 1 wherein thematrix material is selected from the group consisting of celluloseacetate, epoxies, phenols, polyethalene, polyols, polyethers,polystyrene, silicones, urea-formaldehyde, polyurethane and the vinylcompounds.
 3. The device of claim 2 wherein the matrix material ispolyurethane.
 4. The device of claim 3 wherein the polyurethane has fromabout 50 to about 75 percent open cells.
 5. The device of claim 1wherein the liquid is selected from the group consisting of glycerine,sodium chloride, sodium carbonate, sodium nitrate, sucrose, or of otherchemicals having a specific gravity range of about 1.0635 to about1.2296.
 6. The device of claim 5 wherein the liquid is an aqueoussolution of sucrose.
 7. The device of claim 6 wherein the sucrosesolution has a specific gravity of from about 1.0635 to about 1.2296. 8.The device of claim 1 wherein a partial vacuum is drawn on the containersubstantially equal to that drawn on the canned food simulated.
 9. Amethod for artificially reproducing the internal temperature of cannedfoods during processing, comprising:interdispersing permanentlyrecyclable artificial canned food simulators with each batch of cannedfood requiring a heating step during processing, said simulators havinga container housing of substantially similar composition and physicaldimension as the canned food simulated, said container being filled witha porous open celled matrix material and a liquid system uniformlydistributed throughout the matrix material when sealed under partialvacuum, said container being equipped with a suitable thermal indicatorpositioned to externally record the internal temperature from a pointequal distance from all interior walls thereof, the physicalcharacteristics of the matrix material and the liquid system when packedin combination under a partial vacuum being adjusted to accuratelyduplicate the thermal characteristics of the particular canned foodsimulated, simultaneously subjecting the interdispersed simulators tothe identical heat processing procedures as the canned foods beingsimulated, and externally measuring the internal thermal conductivity ofthe food simulated during the heat processing procedures by reading saidthermal indicator.
 10. The method of claim 9 wherein the physicalcharacteristics of the liquid system being adjusted is the specificgravity thereof.
 11. The method of claim 9 wherein a physicalcharacteristic of the matrix material being adjusted is the percentageof open cells.
 12. The method of claim 9 wherein the partial vacuum ofthe container is substantially equal to that drawn on the canned foodsimulated.